During the early 1970s, the price of copper rose to a point where the Lincoln
cent contained nearly one cent's worth of copper. This led the Mint to try
alternate metals, including aluminum and bronze-clad steel. Aluminum was chosen,
and over 1.5 million of these cents were struck and ready for public release
before ultimately being rejected. About a dozen aluminum cents are believed to
still be in the hands of collectors, although they may be considered illegal,
and could be subject to seizure. One aluminum cent was donated to the
Smithsonian Institution.

The 1974 aluminum cent was a one-cent coin proposed by the
United States Mint in 1973. It was composed of an alloy of aluminum and trace
metals, and intended to replace the predominantly copper–zinc cent due to the
rising costs of coin production in the traditional bronze alloy. 1,570,000 were
struck in anticipation of release, but none were released into circulation.
Examples were passed out to US Congressmen in a bid to win favor in switching to
the new alloy. When the proposed aluminum cent was rejected, the Mint recalled
and destroyed the examples. A few aluminum cents not returned to the Mint are
believed to remain in existence. One example was donated to the Smithsonian
Institution, while another was alleged to have been found by a US Capitol Police
Officer. Since the United States Secret Service is tasked with the seizure of
any specimens, the legality of the coins is in doubt.